Oil composition of improved oxidative stability



United States Patent O OIL COMPOSITION OF IMPROVED OXIDATIVE STABILITY ration ofiDelaware N Drawing. Application; June 20, 1952, Serial No. 294,703

4 Claims. (Cl. 25233.6)

The present invention relates to thestabilization ofoils against oxidative deterioration. More particularly, the invention has to do with the preparation of an oleaginous composition comprising a major amount of anormally oxidizable oil and a minor amount, each of an aromatic hydrocarbon compound and of a thiocarbonic acid derivative, each being selected from specific classes of compounds. In accordance with the inven tion, it has been found that the combination of the aforesaid thiocarbonic acid derivative and aromatic hydrocarbon compound has a synergistic anti-oxidant effect.

Among the adverse effects caused by oxidation may be mentioned the formation of corrosive acidic products, sludges, varnishes, resins and other oil-insoluble products, as for example, with mineral oils. Other oils, such as certain synthetic hydrocarbons, tend to further polymerize on oxidation, thus becoming undesirably viscous, while other synthetic oils, for example, the polyalkylene. glycol type, tend to depolyrnerize giving off volatile products. Other oils thicken and become rancid, for example the animal and vegetable fatty oils.

Now I have found that I can substantially increase the resistance tooxidation of these oils and others, whereby their quality and nature are maintained unimpaired over a long period of time either during use or in storage, by the. incorporation in the oil of a small amount of an aromatic hydrocarbon compound in addition to a small amount of a non-acidic thiocarbonic acid derivative selected' from the class consisting of esters, salts, acyl disulfides and thioanhydrides of thiocarbonic acids.

More specifically, the non-acidic thiocarbonic acid derivative is one which is soluble in the oil tothe extent of at least about 0.05%, preferably about 0.1%, by weight of the finished oil, and which has a molecular weight of at least about 150.

In general, the aforesaid thiocarbonic acid derivative may be represented by the following formulas:

In the above formulas, like letters have the same significance. Thus, R and R represent like or different organic groups, such as alkyl groups; Y, oxygen, sulfur, or nitrogen; X, oxygen or sulfur; z, the integer 1 when Y isoxygen or sulfur, and 2, when Y is nitrogen; C, carbon; S, sulfur; and Zn, zinc.

As above indicated, R and R are substituted or unsubstituted alkyl or aryl groups; The substituent groups can be amino, hydroxyl, mercapto, alkoxy, arylox, thio, alkyl, aryl, alkaryl or arylalkyl radicals.

Specific examples of thiocarbonic acidderivatives contemplated-by the invention are zinc di-n-butyldithiocarbamate, zinc i-propylxanthate, zinc sec.-amyltrithiocarbonate, zinc phenyl-n-butyl dithiocarbamate, butyl din-butyl dithiocarbamate, tolyl di-n-butyldithiocarbamate, di-benzyltrithiocarbonate, di-i-butylxanthate, zinc salt of dithiocarbonic acid morpholide, tetramethyl thiouramdisulfide, di-i-propyldixanthogen, and sec.-butylxanthic thioanhydride.

In general, the amount of thiocarbonic acid derivative required for. substantial inhibition of the base oil against oxidation ranges from about 0.03% to about 10% by weight of the finished oil, a satisfactory working amount residing within about the range of 0.1% to 1.0%, with an optimum of about 0.2% by weight of the finished oil.

The aromatic hydrocarbon contemplated by the invention is a naphthalene hydrocarbon. More specifically, it is naphthalene substituted in the alpha position with a hydrocarbon group,.preferably an alkyl group. Other substituent groups can be, in addition to the preferred alkyl group, aryl, alkaryl, arylalkyl and alicyclic hydrocarbon groups. Moreover, hydrocarbon substituents can appear on' other positions of the naphthalene nucleus, provided, however, that at least the alpha position has a substituent hydrocarbon group, as aforesaid. The preferred naphthalene is an u-alkyl naphthalene, in which the alkyl group contains 1 to 20 carbon atoms, preferably 1 to 8 carbon atoms. In addition, the tat-substituted naphthalene is one which is soluble in the base oil to the extent of at least about 5%, and preferably 10% by weight of the oil. In general, the amount of a-hydrocarbon-substituted naphthalene required for substantial inhibition of the base oil resides within about the range of 0.5% to 10.0% preferably 1% to 5% by weight of the oil. A good working amount is 3%, by weight of the oil.

Specific examples of the tit-substituted naphthalenes contemplated by'the' invention are a-methylnaphthalene, and l-amyl naphthalene, 1,2-diamylnaphthalene, l-t-butylnaphthalene, l-octadecylnaphthalene, l-phenyl naphthalene, di-a-naphthyl, u-benzyl naphthalene, a-cyclohexyl naphthalene, u-(prbutylphenyl) naphthalene, and 1,6-dimethylnaphthalene.

Examples of commercially available base oils which may be benefited by the practice of the present invention are highly refined mineral hydrocarbon lubricating oils, which because of theexhaustive refining thereof contain substantially no aliphatic sulfur materials, for example, White oil; Other base oils are synthetic hydrocarbon oils or olefin polymer oils, for example the polybutenes and others derived from the lower olefins, such as ethylene, the propylenes, pentenes, etc., and from the Fischer- Tropsch process. Additional examples of base oils are the polyalkylene glycols of lubricating oil viscosity derived most advantageously from 1,2-propylene oxide, these oils preferably having theterminal hydroxyl groups esterified and/or etherified. Also advantageously treated in ac-- cordance with the invention are the diester oils, that is, those derived from the esterification of certain dicarboxylic acids. for example adipic and sebacic, with alcohols, for example butyl hexyl, and octyl alcohols. Another important class of synthetic base oils are those containing silicon, for example the orthosilicates, preferably those in which the alkyl groups attached to oxygen bound to silicon contain at least three carbon atoms in branched chain structure, for example bis (2-butyl)bis(2- ethyl-l-butyl) silicate, and isopropyl-tris(2-pentyl) silicates; and the polysiloxanes such as hexa(Z-ethyl-lbutoxy) disiloxane.

A convenient method of measuring the resistance to oxidation possessed by the compositions prepared in accordance with the invention is the use of the apparatus and procedure described in Industrial and Engineering Chemistry, vol; 28, p. 26 (1936), wherein the rate of oxygen absorbed at constant pressure by a definite weight of oil is regarded as a measure of the oxidative stability of the oil. According to this procedure, the oil sample is placed in an absorption cell, provided in the bottom with a fine-fritted glass filter'to disperse the oxygen stream, circulating through the system at a constant rate, into fine bubbles. In obtaining the'data hereinbelow appearing, the following modified apparatus and procedure were employed.

The oxidation or absorption cell is constructed of a large glass tube with the head portion having a connection for introducing oxygen, an annular space surrounding the upper end of the tube and a fitting for a removable white oil having a viscosity of about 350 SSU at 100 F. It was prepared from a suitable distillate fraction of a California naphthenic type crude by phenol treatment followed by exhaustive treatment with fuming sulfuric high speed glass stirrer. The annular space contains 5 acid and finished by percolating through fullers earth.

TABLE I Anti-oxidant efiect of tat-substituted naphthalene and thincarbonic acid derivative on white oil Induction Period, Hrs. at 340 F.

Percent Without Without Percent With Thiocarbonic Acid Derivative Thmcal-rbomc a -Amyl Thiocarbonic Tmocarbomc Amyl Acid Na hthalene Acid Acid Naphthalene, Derivative p Derivative, but with Derivative but with Thiocarbonic Amy! 0: -Amyl Acid Nap thalene Naphthalene Derivative 1. Zinc din-butyl dithiocarbamate 0. 1 3. 0 18 1. 7 7. l 2. Zinc i-propylxanthate 0.1 3. 0 18 1. 7 l. 3 3. Tetramethyl thiouramdisulfide 0.1 3. 0 16 1. 7 0.9 4. Di-sec.-butyldixanthogen 0. 1 3. 0 21 1. 7 0.7 5. Butyl di-n-butyldithiocarbamate. 0. 1 3. 0 1. 7 0.2 6. Di-i-propylxanthic thioanhydride. 0. 1 3.0 14 1. 7 0. 9 7. Zinc t-butyltrithiocarbonate 0. 1 3. 0 25 1. 7 2.1

It will be observed from these data that the combined inhibiting effect of each of the thiocarbonic acid derivatives and the aromatic hydrocarbon is far greater than the sum of the effects of the individual additives used separately.

potassium hydroxide pellets for the removal of water, carbon dioxide, volatile aldehydes, etc. The lower portion of the cell which contains the sample to be tested is immersed in an oil bath at a temperature of about 340 F. During the test, the oil sample is rapidly agitated by means of a high speed stirrer and is kept under a pressure In Table II, the polypropyleneglycol oil was an ethylof about 1 atmosphere of pure oxygen, the volume of hexanol-initiated propene oxide polymer of molecular oxygen added being automatically recorded. The time in Weight about 900.

TABLE II Anti-oxidant effect of aromatic hydrocarbon and thiacarbonic acid derivatives of polypropyleneglycol oil Induction Period, Hrs. at 340 F.

Percent Without Without Percent With Thiocarbonic Acid Derivative Thmaibmc a -An1yl Thlocnrbonic Thmcmbmlc 'Amyl Acid Na hthalene Acid Acid haphthalcnc, Derivative p Derivative Derivative, but with And a butAwitli Thioxaggonic a my c Naphthalene Naphthalene Derivative 1. Di-i-propyl dixanthogen 2.1 5.0 2 1 0.0 0 0 2. 'Ietramethylthiouramdisulfide 1.7 5.0 2 8 0.0 0 0 3. Di-n-butvldithiocarbamate-initiated propene oxide polymer (Moi. Wt. about 500).. 10 5. 0 2.4 0. 0 0. 0 4. Butylxanthate-initiated propene oxide polmer (M01. Wt. about 500) 10 5.0 2.4 0. 0 0. 0

Table III is intended to illustrate the anti-oxidant effect on the same base oil as employed in Table I by a representative number of aromatic hydrocarbons and tetramethylthiouramdisulfide.

TABLE III Anti-oxidant efiect of various aromatic hydrocarbons and a thiocarbonic acid derivative on white oil hours required for 100 grains of oil to absorb 1200 cc. of oxygen is called the Induction Period (I. P.), and represents the point at which the sample begins to absorb oxygen or oxidize.

Induction Period, Hrs. at 340 F.

Percent Tet- Without Without Percent With Tetra- Aromatic Hydrocarbon Aromatic igfi g methyl 'Ihtogfi g Hydrocarbon m uramdisulnumm' y disulfide fide and disulfide, but but with Aromatic vgthHAiiglloeitrametglylma 0 y rocuram Hydrocarbon carbon sultlde 1. a-methyl naphthalene 3.0 0. 1 7.0 0.0 0.9 2. a-amvl naphthalene- 3.0 0.1 12.0 0.0 0.9 3. Mixed diamyl naphthalenes (containing a high fraction of a-substituerit) 3. 0 0.1 13. 0 0. 0 0. 9 4, Naphthalene 3. 0 O. 1 1. O 0. I) 0. 9 5. B-amyl naphthalene 3.0 0.1 1. 2 0.0 0.9 6. fl-methyl naphthalene 3. 0 0.1 1. 0 0. 0 0. 9 7. a-phenyl naphthalene 3. 0 0.1 15.0 0. 0 0. 9

The following tabulated data were obtained from a The date accumulated in Table IV illustrates the antinumber of experiments performed in accordance with the i a t effect of aromatic hydrocarbon compounds and test above described. thiocarbonic acid derivatives of the types defined on a In Table I, the base oil employed was a medicinal representative number of base oils.

TABLE IV Anti-oxidant efiect of aromatic hydrocarbon and thiocarbonic acid derivative on various base oils Induction Period, Hrs. at 340 F.

Base on Except as indicated, with 3.0% Except as indicated, Except as indicated,

a-amyl naphthalene and 0.1% only 3.0% a-amylonly 0.1% Di-sec.-

Di-sec.-butyldixanthogen naphthalene butyldizanthogen Polybutene polymer-M. W., about 400 4.1 (5.0% a-amyl naphthalene; 0.0 (5.0% a-amyl 0.0 (0.2% Di-sec.- 0.2% Di-sec.-butyl di-xanthonaphthalene). bngyl-dixanthogen gen Bis(2-ethylhexyl) sebacate 19.0. 1.2. Tetra-(Z-ethylbutyl) silicate 7.8 0.0. Tricresyl phosphate 6.0 1. 4. Polypropylene glycol 1 2.1 myl naphthalene; 0.0 (5.0% a-amyl 0.0 (1.7% Dl-sec.

1.7% Di-sec.-butyl di-xanthonaphthalene). bugyl-drxantlmgen 'en Polypropylene glycol +50%, by volume, mineral b white 011. 1.8 0. 0 0. 0. Hexa-sec.butyldisiloxane 4.3 0.2 0.3.

1 Ethylhexanol-initiated propene oxide polymer, M01. Wt. about 900.

2 Polypropyleneglyool=isooctanol-initiated propane oxide polymer acetate, Mol. Wt. about 600. Mineral white oil =stock prepared as previously described (Columns 3, 4) but with viscosity of about 72 SSU at 100 F.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. An oil composition comprising a major portion of a normally oxidizable oil, together with a total of from 0.03 to by weight of at least one thiocarbonic acid derivative selected from the group consisting of zinc din-butyl dithioearbamate, zinc i-propylxanthate, tetramethyl thiuramdisulfide, di-i-propyl dixanthogen, di-sec. butylxanthogen, bntyl di-n-butyldithiocarbamate, di-ipropylxanthic thioanhydride and zinc t-butyltrithiocarbamate, and a total of from about 0.5 to 10% by weight of at least one hydrocarbon selected from the group consisting of rz-methylnaphthalene, a-amylnaphthalene and u-phenylnapthalene.

2. An oil composition comprising a major portion of a normally oxidizable oil, together With from 0.1 to 1% by References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,160,851 Faust June 6, 1939 2,160,880 Loane June 6, 1939 2,363,880 Lieber Nov. 28, 1944 2,394,536 Denison Feb. 12, 1946 2,412,903 Miller Dec. 17, 1946 

1. AN OIL COMPOSITION COMPRISING A MAJOR PORTION OF A NORMALLY OXIDIZABLE OIL, TOGETHER WITH A TOTAL OF FROM 0.03 TO 10% BY WEIGHT OF AT LEAST ONE THIOCARBONIC ACID DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF ZINC DIN-BUTYL DITHIOCARBAMATE, ZINC I-PROPYLXANTHATE, TETRAMETHYL THIURAMDISULFIDE, DI-I-PROPYL DIXANTHOGEN, DI-SECBUTYLXANTHOGEN, BUTYL DI-N-BUTYLDITHIOCARBAMATE, DI-IPROPYLXANTHIC THIOANHYDRIDE AND ZINC T-BUTYLTITHIOCARBAMATE, AND A TOTAL OF FROM ABOUT 0.5 TO 10% BY WEIGHT OF AT LEAST ONE HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF A-METHYLNAPTHALENE, A-AMYLNAPTHALENE AND A-PHENYLNAPTHALENE. 